Apparatus for conditioning air



May 16, 1933.

C. F. SHADLE APPARATUS FOR CONDITIONING AIR Original Filed April 1, 19502 Sheets-Sheet l mm. v a m m I I I X g n WWI W QF a w; I 5 I I y 1933.c. F. SHADLE 1,909,227

APPARATUS FOR CONDITIONING AIR Original Filed April 1, 1930 2Sheets-Sheet 2 em, as pm 5 3 a. w m P Q O O O O O in .T a: a 3 iv(Ittorneg Patented May 16, 1933 PATENT OFFICE CLINTON 1 SHADLE, O1WATEBTOWN, NEW YORK APPARATUS FOR CONDITIONING AIR continuation ofapplications Serial Ion. 440,809 and 440,810,11ed April 1, 1930. Thisapplication filed April-11, 1931. Serial No. 529,456.

This invention relates to apparatus for drying gases, and particularlyair, for induspressed air is Widely used in industry, and

' in many ofthe fields of use, the presence of moisture in substantialquantity entails serious difliculty. For example, in spraying paint bythe use of compressed air, serious harm can be done by water sprayedwith the air. 35 Unless the compressed air is freed of water, there is atendency for condensed moisture to accumulate in the system, and whenthis has accumulated in quantity it may be picked up by the dischargingair and become a source of loss and delay.

Compressed air motors are subject to frequent stoppage by frost whenused with air not properly freed of moisture. Similarly, in air brakesof various types, the deposition of moisture throughout the system hasbeen a frequent cause of trouble and expense. When atmospherictemperatures fall below the freezing point of water, the possibilitythat the moisture will freeze and impair o1 3a prevent the operation ofthe brakes, is a source of serious danger. Consequently, any apparatuswhich will reduce the moisture content of air to a low point, at acommercial rate, and without undue expense, is of substantial economicimportance.

There are two physical principles which .may be availed of to reduce themoisture content of gases. The total weight of-water which will exist/asvapor in a given volume is dependent'upon vapor pressure which is afunction of temperature. The presence or absence of a gas in the volumedoes not materially affect the weight of water which will exist asvapor, nor does the density of that i gas have material effect. Hence,if saturated air, for example, be compressed and if its initialtemperature be restored, itrwill reject moisture, for as the volume isreduced the amount of saturated vapor which can exist at a giventemperature is similarly reproximate the theoretical possibilities. Thisduced. If the volume and temperature both be reduced from the initialvalue, it is obvious that a given volume will contain an increasingweight of air and a decreasing weight of moisture, so that the ratio ofmoisture to air will diminish.

Attempts to avail of these principles on a commercial scale have not, sofar as I am advised, secured results which even closely apisparticularly true where efforts are made to reduce the-absolute humidityto a very low value.

As the most important field for devices of the characterhere underdiscussion is in the dehumidification of air, reference will hereafterbe made to air, but with the understanding that-the same principlesapply to the treatment ofgases in general, and that the discussion isillustrative.

In prior artair conditioners reliance has been placed on refrigerationof the air to condense the water vapor mixed therewith. Two generalmethods of refrigerating the air have been used; one passes the air overtubes or other surfaces which are maintained at a low temperature byrefrigerating machines, and

. contemplates the formation of frost in large quantity the othersubjects the air to contact with sprays of refrigerated water or brine.The latter scheme is not suitable for extremely low temperatures. It hasbeen proposed, particularly in the second type of device, to make use ofthe so-called eliminators. These ordinarily are merely sheet metal baesflooded with refrigerated water. Their function is to entrap and removefrom the, air suspended droplets of water.

Conditioners of the types just mentioned are satisfactory forconditioning air for buildings, for the reason that in such case anextremely low relative humidity is not necessary. Efl'orts to avail ofmodified forms of such a paratus'to deliver air of low relativehumidity, have been subject to the difliculty that the absolute humidityof the delivered air materially exceeded the value corresponding to thetemperature attained in the conditioner. Any conditioner in which frostforms in quantity must be shut down periodi- 109 cally for defrostingand is inefficient except when free of frost.

The present invention is based on the discovery that'there is a tendencyfor water condensing from the vapor stage in air, to remainin'suspension in the air in the form of droplets which are so minute asto be invisible. These droplets do not precipitate readily, and,consequently, flow with the air through the conditioning device, and areunaffected by conventional eliminators. These minute droplets readilyreevaporate upon increase in volume of the air. or upon rise in itstemperature, or both. While these droplets are of such a character thatthey can not be successfully precipitated by conventional eliminators orcentrifugal separators. they have an inherent tendency to grow in sizeif the air be subjected long enough to the low temperature which inducescondensation. In this way it is possible to develop the droplets to asize at which they may be eliminated by mechanical means.

Most such mechanical means depend on inertia effects which produce aselective tendency of the heavier water droplets to move out of the airstream and form a water film on surfaces upon which they impinge. As atypical example of such separators there may be mentioned conventionalcentrifugal separators.

The present invention involves the idea of promoting the growth of thewater droplets to a size permitting a mechanical separation of thedroplets from the air, and at the same time minimizing the actualcontact of the water droplets with the refrigerated surfaces,particularly where those surfaces are cold enough to cause freezing. Thedroplets are then separated from the air after the air has passed therefrigerating surfaces so that the separation takes place at a pointwhere the tendency toward frost formation or freezing is less than it isadjacent the refrigerating surfaces.

Generally stated. the air is sharply cooled below its dew-point bypassing it in proximity to a refrigerated surface or surfaces, andkeeping the air. so far as is possible, out of contact with suchsurfaces. When this is done the minute water droplets commence to formand remain suspended in the air. The droplets grow in size at a ratewhich rapidly increases because of the rapid increase in surface of eachdroplet with progressive increase in diameter. Each droplet receivesheat from the vapor condensing upon it and radiates that heat to theadjacent refrigerative surface without contact with that surface. Ifsuflicient time be allowed, under the conditlons just mentioned, thedroplets ultimately attain a size favorable to mechanical separationfrom the 'air.

Only those droplets which actually contact the refrigerating surfacewill deposit as fro t 011 such surface and the invention contemplatesthat the contact of droplets with any refrigerating surface which isbelow freezing temperature, will be minimized, so far as practicalstructural considerations permit. The apparatus is so arranged that whenthe droplets have reached a size favorable to mechanical separation, andbefore they commence to precipitate by gravity in any considerablequantity, they enter a mechanical separator and are mechanically removedfrom the air stream.

It follows that any refrigerative coolerat freezing temperature must bedesigned to favor the transfer of heat to the refrigerative surface byradiation, and to-minimize actual physical contact with therefrigerative surface. Consequently, the form and spacing of therefrigerative units are selected to favor radiation. The velocity of airflow past the refrigerative surfaces is kept at as low a value as ispracticable in order to secure no nturbulent flow, or, as close anapproximation thereto as is practicable. Turbulence is further minimizedby the adoption of stream line forms, to the end that eddying tendenciesmay be minimized.

In some cases a single refrigerative unit is used. Where extreme drynessis desired it is possible to use a plurality of refrigerated surfaces towhich successively the air radiates heat, each successive unit-being ata lower temperatur than its predecessor. The air leaving therefrigerative unit or series of units, is immediately treated in amechanical separator to remove the water droplets. The best results sofar secured have been had with a separator of the centrifugal type.

\Vhere its use is feasible, economies can be effected by the use of aregenerative heat interchanger in which cold air leaving the moistureseparator passes in heat exchanging relation with the warm untreated airflowing to the refrigerative device. There are practical limits to theuse of the regenerative interchanger. The untreated air is heavilycharged with moisture and the regenerative interchanger, becauseof itsdesign to secure high heat transfer, is apt to freeze up if thetemperatures are below freezing. In such cases a regenerativeinterchanger should not be used.

Counterflow in such interchanger, while desirable from the standpoint ofmaximum heat exchange, is often impracticable because of the increasedtendency to freeze up. Consequently, in most cases where theregenerative interchanger is used, the flow is concurrent, that is, bothair streams flow in the same direction.

The applicability of the'invention to different conditions will now bedescribed in connection with the accompanying drawings, which illustratepractical embodiments of the invention, using one or more refrigerativestages and usin difi'erent types of regenerative heat interc angers.

In the drawings' Fig. 1 is a vertical longitudinal section of a devicehaving a single refrigerative stage anda regenerative heat interchangerof the counterflow type.

Fig. 2 is a section on the line 2-2 of Fig. 1.

Fig. 3 is a vertical axial section of the moisture separator shown inFig. 1.

Fig. 4 is a view similar to Fig. 1, but showing a device having tworefrigerative stages and.a regenerative interchanger of the concurrentflow type.

Fig. 5 is a section on the line 5-5 of Fig. 4.

Fig. 6 is a fragmentary view showing the use of vbafiles in the airpassages in the first refrigerative stage.

Fig. 7 is a fragmentary view showing how the connectionsv of theregenerative interchanger may be reversed in Figs. 1 and 4.

Such reversal would change the interchanger of Fig. 1 to the concurrentflow type and would chan e the interchanger of Fig. 4 to the counter owtype. Referring first to Figs. 1, 2 and 3:

11 represents a cylindrical shell which has a tapered inlet head 12 withinlet connection 13 and a tapered outlet head 14 with outlet connection15. The purpose of using the tapered heads is to give a gradual changein section and thus reduce eddying tendencies: The eddying tendenciesproduce a less disturbing effect at the exit end, and for this reasonthe exit head 14 is given a wider flare than the entrance head 12 tosave space. Where space permits, it is advisable to make the chan es incross section as gradual as possible, cause the ideal conditioner wouldhave the closest possible approach to non-turbulent flow through theshell 11.

Mounted in' the shell is a cooling element,

consisting of a plurality of flat leaves or.

plates 16. These leaves or lates are hollow, as indicated in Fig. 2, andt e opposite walls are braced together against both compressive aridexpansive stresses, by stays, indicated generally at 17 lit will beunderstood that the air to be treated, in the illustrated device, willarrive under a pressure of, for example, approximately 150 pounds persquare inch and that when the evaporative refrigerating unit is inoperation, the suction pressure within the leaves may be quite low. Onthe other hand, when the compressor is shut down, so that onlyatmospheric pressure will exist within the shell 11, the refrigerate;unit is also likely to be shut down, at wich time the vapor pressure inthe plates 16 will riseto a substantial value. For this reason the stays17 should be arranged to resist stresses inboth directions.

The edges of the leaves 16 are rounded, so far as possible, as isclearly illustrated in the drawings, and they are spaced above thebottom of the shell 11, as is clearly indicated in Fig. 2 so thatwhatever moisture is precipitated in the shell 11 will not be in contactwith the leaves 16 but will be drained away by the connection 18. Thequantity of moisture so precipitated is kept as small as possiblebecause of its tendency to freeze. The connection 18 is shown asequipped with a hand operated valve 19, but it is within the scope of myinvention to use automatic valves of any suitable type in place of thevalve 19. As these would assume various different forms, according tocircumstances,

it is deemed suflicient to illustrate any suitable valve, and a handoperated valvecan be used to secure the desired result.

While it is within the scope of the present invention to circulate anyrefrigerative or heat absorbing liquid through the leaves 16, it isconsidered to be simpler and better to make use of a volatile liquidrefrigerant, siich, for example, as sulphur dioxide or methyl chloride.

This refrigerant liquid is supplied through aliquid line 21 which leadsto a I manifold 22. The manifold 22 communicates with all the leaves 16and the refrigerant is supplied by any suitable known means in such away as to maintain the leaves 16 substantially flooded with the liquidrefrigerant. The vapor evolved in the leaves 16 flows out through asecond manifold 23 to which is connected the suction line 24. While theleaves 16 may be maintained at any suitable temperature, dependent onthe degree of dryness desired, my invention attains its greatest utilityin those cases where the leaves are maintained at temperaturessubstantially below the freezing point of -water.

Air enters at 13 and flows to the right between and around the leaves,giving up its heat by radiation, and, in some degree, by 1 directconduction to theleaves. Some moisture may be precipitated but thequantity normally is small. The arrangement is favorable to a minimumcontact of the moisture laden air with the leaves. of the air betweenthe leaves its temperature will be greatly lowered by radiation to theleaves, with the result that droplets will form and grow, and by thetime the air flows In the travel out through the connection 15, willhave reached a size'such that theyv may be separated by mechanical meansfrom the air.

The preferred mechanical means is a centrifugal separator, indicatedgenerally by the numeral 25 applied to its case. This is illustrated asconnected by an elbow conilection 26, which is combined with the coverof the case 25, to the outlet 15. The centrifugal separator comprises acircular seriesofblades 27 in secant arrangement. Air entering throughthe elbow 26 and flowing outward between the blades 27, is iven awhirling motion within the centri ugal case 25. The droplets which areprojected, partly against the blades and partly against the interiorsurface of the shell 25, coalesce and flow down to the bottom of theshell where they are retained by an annular dam' 28 which surrounds theoutlet connection 29. The air flows beneath the bafile 31 which connectsthe lower ends of the blades' 27, and over the dam 28 to the outlet 29.The precipitated water is drawn off through the connection 32, which, asshown in Fig. 1, is controlled by a valve 33.

The mechanism so far described is heavily insulated against the entranceof heat, the insulation being shown at 34. In many instances theconnection 13 would receive the air coming directly from the compressoror coming from the compressor by way of an atmospheric cooler, and thedried air would be piped from the connection 29 to the point of use. Asthe air leaving the conditioner is generally too cold for use, economiescan be effected by passing the entering air and leaving air in heatexchanging relation with each other. For this reason a regenerative heatinterchanger of the shell and tube type is sometimes used, and, like theshell 11 and the separator 25, is enclosed in the main body ofinsulation 34.

This interchanger comprises a cylindrical shell 35 closed by two heads36 which are spaced from corresponding tube sheets 37. Expandedinto'these tube sheets are a plurality of tubes 38 which connecttogether the spaces intervening between the head 36 and the tube sheet37 at the two ends of the caslng. Air coming from the compressor, eitherdirectly or through an atmospheric cooler, enters the interchangerthrough a connection 39. It flows thence through the tubes 38 and theconnection 41 to the connection 13 at the entrance end of the shell 11.Moisture precipitated in the tubes is drawn off through connections 42which are controlled by valves 43. These valves 43, like the valves 33and 19, might be controlled automatically, or in any suitable way, sofar as the present invention is concerned.

Air leaving the separator through the con nection 29 flows by way ofpipe 44 to the interior of the shell 35 so as to flow around the outsideof the tubes 38, and passes from the shell to a point of use through theconnection 45. A spiralbafiie 40' directs the flow within shell 35.

The regenerative interchanger shown in Fig. 1 is of the counterflowtype, that is, the leaving air flowing around the tubes 38 and theentering air flowing through the tubes 38 flow in generally oppositedirections. Concurrent fiow can be secured by a simple reversal of thepositions of the connections 44 and 45. This is shown in Fig. 7 wherethe 0011 nection 44 is at the right end of the shell 35 and theconnection 45 is at the left end.

Regenerative interchangers are known, and interchangers of theconcurrent and counter'current flow types are both known. No novelty ishere claimed for the interchanger broadly.

As suggested above, I contemplate the use of a plurality ofrefrigerative stages instead of the single one shown in Fig. 1, and astructure embodying this idea is shown in Figs. 4 to 6. There are twocases which differ according to whether the first stage is 01' is notoperated below freezing temperature. If the first stage is operatedbelow freezing temperature nonturbulent flow is used as in Figs. 4 and5. If the first stage is above freezing temperature, baffles 47 areadded to give turbulent flow and hence more effective heat transfer, asshown in Fig. 6.

In the drawings the parts of the two refrigerative elements are giventhe same numerals, as similar parts in Fig. 1, with the subscripts a andb, for the purpose of distinguishing the two units.

There isa simple pipe connection 46 from the discharge connection 15 ofthe first unit to the inlet connection 13 of the second unit. There is asingle drain connection 18 with valve 19 which serves both of the shells11 and 11 and the discharge connection 15 for the second stage leadsdirectly to a separator 25, identical with that already described. Theinterchanger, when an interchanger is used, is identical with thatdescribed above, and the parts are similarly numbered in Figs. 1 and 4.The connections shown in' Fig. 4 are for concurrent flow, the

inlet and discharge connections being reversed end for end in Fig. 4relatively to Fig. 1. Counter-flow could be secured in Fig. 4 byreversing the connection 44 and 45, as indicated in Fig. 7.

There are separate suction lines leading from the suction manifold 23 ofthe first unit and the suction. manifold 23 of the second unit. This isto permit the two units to be operated at different suction pressures,and, consequently, at different temperatures. It is immaterial how thisdifference is effected. Known ways of doing so are to use separatecompressors for the two evaporators, or to throttle one suctionconnection, or

to use the dual suction connection system -covered by certain patents toGardner Voorhees,

for example, Patent No. 982,463, dated J anuary 24, 1911.

Ordinarily the purpose of using two refrigerative stages in series is toobtain a lower temperature and consequently a lower absolute moisturecontent. The first unit commonly is at or about freezing temperature,though it may be decidedly below the freezing temperature without dangerof un due frosting if the non-turbulent flow char- -acteristics areensured. The second unit is decidedly below freezing temperature. If thefirst unit be operated above freezing temperature, staggered baflies 47are used to en-- sure that turbulent flow is secured. In such case theuse of tapered or conical heads 14 is not necessary. f

The efl'ect of using a plurality of refrigera tive stages (two beingshown) at temperatures which become progressively lower in the directionof the air flow, is to cool the air economically to a relatively lowtemperature and to carry this out over a relatively longflow path, sothat the water droplets will have an opportunity to grow to the desiredsize. In the two stage conditioner, as in the single stage conditioner,the object is to stimulate the growth of vwater droplets to a size atwhich they are capable of mechanical separation, and then effect thisseparation at a point beyond the refrigerative stages, so that thetendency to form frost will be minimized.

The use of the interchanger in the structure of Fig. 4c is subject toexactly the same limitations as is its use in the-structure of Fig. 1,but the limitations are more severe, because the exit temperature of theair is lower.- Gonsequently, the average temperature in the interchangertends to be lower.

It will be observed that the flow in the interchanger is distinctlyturbulent in character, the velocity throu h the tubes being necessarilyhigh and t e flow around the tubes being baflled and irregular. Y

The illustration in the drawings is to a considerable extentdiagrammatic, and various changes, to accommodate the a paratus toparticular conditions, are contemp ated. One of the greatest problemsencountered in air brake practice is that imposed by the very limitedspace available onthe locomotive. These requirements have led to theadoption of e leaf type evaporator, and this evaporator is an portantfactor in success in all installations where space isthe controllingconsideration. r

In apparatus as actually used the air was compressed by a two stagedirect acting air pump of the type 1| u only usedin air brakeinstallations, and was-delivered by the pum under a pressure of theorder of 150 poun sgage. The temperature at discharge approached 500 F.at times. 'lhe heat of compression was largelyremoved by passing the airthrough an atmospheric cooler composed of a zig-zag pipe exposed to thesurrounding air. This cooler delivered the air to the apparatus abovedescribed, and the dried air was delivered to the. usual receiver, knownin air brake practice as a main reservoir. Various difierenttemperatures were maintained in the cooling units, particularly thesecond.

Strictly non-turbulent flow is diificult, if not impossible to attain,but low lineal velocities are essential, and as the velocity is loweredthe desired condition is approached. For commercial use a linealvelocity of about 150. feet per minute, has been found practicable, andat such velocities satisfactory results have been secured.

What is claimed is, 1. An apparatus for removing water from a mixture ofwater vapor and a gas, comprising a shell designed to minimize thechanges of cross section and to provide gradual changes of cross sectionwhere such changes are necessary; inlet and discharge connections atopposite ends of said shell; a refrigerative cooler mounted in saidshell comprising a plurality of substantially vertical spaced leaves ofapproximately stream line form extending in the general direction offlow through said shell; connections for conducting refrigerating fluidto and from said leaves and a mechanical moisture separator interposedin the path of outflow from said shell. v

i 2. An apparatus for removing water from a mixture of water vapor and agas, comprising a shell designed to minimize the changes of crosssection and to provide gradual changes of cross section where suchchanges are necessary; inlet and discharge connections at opposite endsof said shell; 'a refrigerative cooler mounted in said shell comprisinga plurality oi?- substantially vertical spaced leaves of approximatelystream line form extending in the general direction of flow through saidshell; connections for conducting refrigeratin fluid to and from saidleaves; and a. centri ugal moisture separator interposed in the path ofoutflow from said shell. s 1

3. An apparatus for removingwater from a mixture of water vapor and agas, comprising a shell designed to minimize the changes of crossgradual changes of cross section where such changes are necessary; inletand d1scharge connections at opposite ends of said shell; arefrigerative coo er mounted in sa1d shell comprisin a plurality ofsubstantially vortical space leaves of approximatelystream line formextending in the general direction of flow through said shell;connections for conducting refrigerating fluid to and from said leaves;a mechanical moisture separator interposed in the path of outflow fromsaid shell; a heat intercha the mixture flowing to said shell an thedried gas leaving said separator pass in heat exchanging relation out ofcontact w th each other; and means for draining precipitated moisturefrom said interchanger.

4. 'An apparatus for removing Water from a mixture of water vapor and agas, com-' prising a shell designed to minimize changes of cross,sectlon and to provide gradual'changes of cross section .where suchchanges are necessary; inlet and discharge section and to provide ire erthrou h which connections at opposite ends of said shell; arefrigerative cooler mounted in said shell comprising a series ofsubstantially vertical spaced leaves of approximately stream line formextending in the general direction of flow through said shell;connections for conducting refrigerating fluid to and from said leaves;a centrifugal moisture separator interposed in the path of outflow fromsaid shell; a heat interchanger through which the mixture flowing tosaid shell and the dried gas leaving said separator pass in heatexchanging relation out of contact with each other; and means fordraining precipitated moisture from said interchanger.

5. An apparatus for removing Water from a mixture of water Vapor and agas, comprising a plurality of shells connected in series with eachother, the second of said shells being designed to minimize the changesof cross section and to provide gradual changes of cross section wheresuch changes are necessary; refrigerative coolers one mounted in each ofsaid shells, said coolers each including a plurality of substantiallyvertical spaced leaves of approximately stream line form extending inthe general direction of flow through the shell; connections forconducting refrigerating fluid to and from said leaves, the connectionsfor the leaves in one shell being independent of the connections for theleaves of another shell, whereby the leaves may be operated atcharacteristically different temperatures in the various shells; and amechanical moisture separator interposed in the path of outflow from thelast shell of the series.

6. An apparatus for removing water from .a mixture of water vapor and agas, comprising a plurality of shells connected in series with eachother, each of said shells being designed to minimize the changes ofcross section and to provide gradual changes of cross section where suchchanges are necessary; refrigerative coolers one mounted'in each of saidshells, said coolers each including a plurality of substantiallyvertical spaced leaves of approximately stream line form extending inthe general direction of flow throu h the shell; connections forconducting re rigerating fluid to andfrom said leaves, the connectionsfor the leaves in one shell being independent of the connections for theleaves of another shell, whereby the leaves may be operated atcharacteristically different temperatures in the various shells; and amechanical moisture separator interposed in the path of outflow from thelast shell of the series.

7. An apparatus for removing water from a mixture of water vapor and agas, comprising a plurality of shells connected in series with eachother, each of said shells being designed to minimize the changes ofcross section and to'provide gradual changes of cross section-Where suchchanges are necessary; refrlgerative coolers one mounted 1n each of saidshells, said coolers each includleaves, the connections for the leavesin one shell being independent of the connections for the leaves ofanother shell, whereby the leaves may be operated at characteristicallydifferent temperatures in the various shells; and a centrifugal moistureseparator interposed in the path of outflow from the last shell of theseries. 1

8. An apparatus for removing water from a mixture of water vapor and agas, comprising a plurality of shells connected in series with eachother, each of said shells being designed to minimize the changes ofcross section and to provide gradual changes of cross section where suchchanges are necessary; refrigerative coolers one mounted in each of saidshells, said coolers each including a plurality of substantiallyvertical spaced leaves of approximately stream line form extending inthe general direction of flow through the shell; connections forconducting refrigerating fluid to'and from said leaves, the connectionsfor the leaves in one shell being independent of the connections for theleaves of another shell, whereby the leaves may be operated atcharacteristically different temperatures in the various shells; amechanical moisture separator interposed in the path of outflow from thelast shell of the series; a heat interchanger through which the mixtureflowing to the first shell of the series and the dried gas leaving saidseparator pass in heat exchanging relation, out of contact with eachother; and means for draining precipitated moisture from saidinterchanger. V i

9. An apparatus for removing water from a mixture of water vapor and agas, comprising a plurality of shells connected in series with eachother, each of said shells being designed to minimize the changes ofcross section and to provide gradual changes of cross section where suchchanges are necessary; refrigerative coolers one mounted in each of saidshells, said coolers each including a plu rality of substantiallyvertical spaced leaves of approximately stream line form extending inthe general direction of flow through the shell; connections forconducting refrigerating fluid to and from said leaves, the connectionsfor the leaves in one shell being indeoutflow from the last shell of theseries a heat interchanger through which the mixture flowing to thefirstshell of the series and the dried gas leaving said separator pass inheat exchanging relation, out of contact with each other; and means fordraining precipitated moisture from said interchanger.

10. An apparatus for treating air, comprising means defining a passage;a refrigerating unit in said passage and adapted to be maintained nearthe freezing point of water but above that temperature at which frostwill form; battles in said passage arranged to produce turbulent flowthrough the passage; means defining a second passage to which the firstdelivers, said second passage being so defined as to have gradualchanges of cross section, where such changes are necessary, to minimizethe tendency toward turbulent flow; a plurality of plate-likerefrigcrating units mounted substantially vertically and in spacedrelation in said second passage; a moisture separator to which saidsecond passage delivers; means for draining moisture from both saidpassages; and means for delivering refrigerating fluid to andwithdrawing it from said cooling units.

11. Apparatus for drying air, comprising two refrigerating devicesthrough which the air to be dried passes in series, the first 1 beingarranged for turbulent flow and maintained at a temperature near to butslightly above the point at which frost will deposit, and the secondbeing designed for non-turbulent flow and adapted to be maintained attemperatures below the point at which frost tends to form; and amechanical moisture separator to which the second refrigerating devicedelivers.

12. Apparatus for drying air, comprising two refrigerating devicesthrough which the air to be dried passes in series, the first being 0arranged for turbulent flow and maintained at a temperature near to butslightly above the point at which frost will deposit, and the secondbeing designed for non-turbulent flow and adapted to be maintained attemperatures below the point at which frost tends to form, and acentrifugal moisture separator to which the second stage delivers. Intestimony whereof -I have signed my name to this specification.

CLINTON SHADLE. V

